1. Field of the Invention
The present invention relates to an endoscope apparatus, and more specifically, to an electronic endoscope apparatus provided with a solid-state image sensor, such as a charge-coupled device.
2. Description of the related art including information disclosed under .sctn..sctn. 1.97-1.99.
Conventionally, an electronic endoscope contains a solid-state image sensor, such as a charge-coupled device, in its distal potion. An image of an object in the body cavity is electrically sensed by the image sensor, and an image signal delivered from the sensor is transmitted through a transmission line of the endoscope to a monitor, and is displayed as an image thereon. According to such an electronic endoscope apparatus, an endoscope control device, including e.g. a light source, video processor, etc., is provided independently of the electronic endoscope. The control device drives the image sensor, converts the image signal from the sensor into a standard television signal, and supplies the TV signal to the monitor.
In the endoscope apparatus as described above, electronic endoscopes of various types are used having insertion sections of different lengths, depending on the region to be observed. Thus, the length of the signal transmission line, extending from the solid-state image sensor at the endoscope distal portion to the endoscope control device, varies depending on the type of the endoscope used. If the transmission line is too long, the waveform of a driving pulse may possibly be distorted by a signal conductor, so that the image sensor sometimes cannot be accurately driven by the driving pulse. Moreover, the transmission of the image signal from the image sensor through the transmission line is delayed by the transmission line.
In general, an image signal from the solid-state image sensor is a scattered pulsative signal, which is held or clamped and converted into a continuous signal by the video processor in the endoscope control device. If the image signal is delayed, therefore, it is held with a time lag behind a predetermined timing, so that an accurate signal cannot be obtained from the video processor. The degree of waveform deterioration by the signal transmission line and the delay time depend on the length of the transmission line. The transmission line length varies depending on the type of the endoscope apparatus used. Presently available endoscope apparatuses include, for example, endoscope apparatuses in which a CCD TV camera is mounted on an eyepiece portion of an endoscope without a solid-state image sensor therein, apparatuses using an electronic endoscope, electronic versions of different lengths. Thus, the transmission-line delay time varies according to the endoscope apparatus used.
In order to solve these problems, a suggestion has been made that the endoscope control device or endoscope be provided with a compensation circuit for compensating the image signal depending on the type of the endoscope used. If the endoscope control device is furnished with such a signal compensation circuit, however, it is complicated in circuit configuration, and has reduced reliability. If the compensation circuit is attached to the endoscope, on the other hand, a number of compensation means must be provided for various types of endoscopes, thus entailing increase in the number of components used in the apparatus.